How should we define “Genetic Value” anyway,
on an imputed index from pedigree and DNA, or from the actual, realized performance of our cows over their lifetime
of production?
I recently updated analyzation for a thoughtful career dairyman in west central
Michigan, who had recently bought cows from a nearby herd dispersal. Of the four cows he brought home, two have
already left his herd within months of their purchase. In spite of eyeballing them at the farm of
origin, they proved unable to adapt to his environment (and it is a well-managed, cow-friendly
environment). Lack of adaptation to an environmental change is a key
reason auction barn cows only last an average 1.5 lactations in their new home.
This dairyman has cows within his herd that have achieved seven
lactations and do not show any signs of impending failure. These are the cows he would most like to
be dams of future herd replacements.
He believes strongly that “cows with longevity survival produce
heifers with the same ability”
[especially when care is taken in mating as in his use of “aAa”
analysis]
What he particularly likes about these successful matured cows is that, as the
ME tables always predicted, they tend to milk 30% more in fourth, fifth, &
sixth lactations than they did with first lactation (20% more than second
lactation, 10% more than third lactation).
This brings up the key fallacy in the various Genomic mating concepts built
around use of sexed semen to produce all your future replacements from
“unproven” virgin heifers, on the basis of their higher Genomic (DNA +
pedigree) rankings. The common
weakness with ALL such sales promotions is that your cows are treated
as having no “breeding” value whatsoever. All the progress your herd needs to make then
has to come from selection of sires on indexes… which is a blatant
contradiction of the known biology, in which 50% of the genes in
your calves’ genotype come from the dam – a gene contribution equal
to what is received from her sire.
Genetic progress on pedigree index is illusory if cows are turning over
(leaving the herd) in the third lactation, as is the national average. The genetic selection for high peaks in
first lactation and an acceleration of the growth of heifers has had the effect
of shortening herdlife—ie, cows are ”matured” in second lactation and “aging”
(physically failing) in third lactation.
The sort of heifer that proves to be a more regular-breeding, long-term
high lifetime cow will have a flatter and more persistent lactation curve than
the “accelerated” herdmate… and she has inherited that from her longer lifetime, successfully adapted
mother who preserved that from her own ancestry based in
earlier generations of more broadly-based selection approaches. These are the only animals that live up to
the “ME” predictions given to the records of all tested heifers.
It appears to take all the first lactation and part of the second
lactation production to pay back costs of raising heifers. To be
a profitable dairy, it takes lots of mature and maturing cows…
What is the “PTA” value of realized maturity?
So you might get 20,000 pounds of milk in the first lactation from a typical
TMR-fed nutritionist balanced ration.
30% more at maturity is 6000 pounds more… This is twice the PTA milk value of
the very highest sires in AI today.
Thus the matching of cows to sires under the “aAa” system which is proven to
provide longer herdlife replacements, has a PTA Milk “value” equal to the
highest of Genomic imputations… in other words, you want to see all that paper
progress realized in your future herd performance.
The average USA cow on DHIA test produces milk for 2.5 lactations (this
varies by geography). This means the
average cow leaving during third lactation has overstated her
sire’s PTA value by its calculation from Mature Equivalent (ME) factors by 15%.
For an AI sire to live up to the imputed ME production levels in his
genetic evaluation across all his offspring, he would need to have a PTA- PL
(Productive Life) value of + 7.0. I am unaware of any current progeny evaluated sires exceeding a PL value
of +3.5.
While there are plenty of young Genomic sires with imputed PTA values well in
excess of those achieved once sires have progeny in production for evaluation,
the industry must come to grips with the biological reality: Possession of desired
“marker” genes associated with PTA traits has no direct causation to the
complex physiological and metabolic processes which any cow brings to her “real
world” environment within a physique that must be capable of all desired cow
functions (even feed
consumption-- production—component synthesis—reproduction and calving recovery—completion
of physical growth— immune function --stamina and sustained vigor—mobility –
social herd adaptation – human interaction).
Most of this list has no direct link to any traits measured in PTA form.
Why is it so hard for realized generational progress (as documented in the five-year step-up of
“the genetic base” from national herd averages)
which has been no more than 100 pounds of milk yearly (500 PTA pounds
per five-year “base change”) all through the PTA calculation era—to approach
the expectations of sire PTA values of 1000 to 2000 pounds milk deviations?
Actually, data from AI sired cows in the Netherlands shows that the
highest ranking of USA milk bulls only provide their PTA estimates in their
first lactation deviations: typically
only half as much deviation in second lactation; and then deviation disappears
in third lactations. Milk production
over their lifetime is not increasing: it is merely accelerated in their first lactations at the
expense of a longer-life productivity.
[Data sourced from CRV dutch DHI dairy database]
It must be admitted that “genetic value” as currently calculated only answers
maybe one third of what is required in selection of economic genes, matching
cows to bulls on characteristics of the desired physique, and creating the
rearing environment to harvest quality replacements.
